In the construction and pile driving industry, workmen use hand-held pneumatic hammers to drive small diameter pipe piles into the ground. These small diameter piles are generally referred to as "pin pile" or "needle pile." Throughout the disclosure, reference shall be made to these piles by referring to them as needle piles. Needle piles are metal pipes of relatively small diameter, for example, from one to four inches, which are driven into the ground in an array of piles. The embedded piles form a support structure that, for example, is used to support a column member of a building.
Compressed air powers hand-held pneumatic hammers. In typical manually-operated pneumatic hammers, a force of approximately ninety foot-pounds is created to drive the needle pile into the ground. In operation, a workman drives a needle pile into the ground by bracing his feet adjacent the pile and holding the hammer above the needle pile with the hammer head maintained in contact with the top end of the pile. As the hammer pounds the pipe, the workman guides the hammer along with the pipe toward the ground while maintaining his footing as best he can. After the workman has driven a few piles into the ground, he often stands atop these piles to position himself to drive additional piles into the ground.
Alternatively, in some situations, the length of pile is greater than the length that can be controllably driven into the ground by the workman standing on the ground. For these situations, temporary scaffolding is erected on which the workman climbs to position the hammer on the top end of the longer length of needle pile. As the pile is being driven, the operator climbs down the scaffolding until the pile is driven sufficiently into the ground.
This hand-held hammer method of driving needle pile into the ground is not only labor intensive and time consuming, but is dirty, exhausting, and often dangerous for the operator of the hammer. The operator exerts a great deal of energy to maintain the hammer in line with the end of the needle pile, while attempting to maintain his footing, either on broken ground, temporary scaffolds, down in a trench, or in other adverse conditions. Because the hammer head of the hand-held pneumatic hammer is a relatively powerful tool, it can easily injure the operator or other workmen under such conditions. Consequently, the manually-operated pneumatic hammer method of driving needle pile creates a significant risk of injury to operating personnel.
In addition, pneumatic hammers are limited in the amount of force they can generate to drive needle pile. Generally, as mentioned, compressed air powered hammers generate approximately ninety foot-pounds of force. With this amount of force, driving needle pile can be a time-consuming operation. Often it can take up to an entire day to drive a single needle pile into certain types of earth.
Pile driving crane apparatus are also known for driving large diameter piles into the ground. Such cranes are used to drive concrete, steel, or wood piles of relatively large diameter, for example, eight to ten inches. Pile driving cranes typically include a large frame that supports a vertical mast or guide beam, which guides a hammer weight down along the length of the beam. The vertical mast or beam of a pile driving crane can exceed thirty feet in height. The size of these vehicles is necessary to generate and control the forces necessary to drive large diameter pile into the ground. The hammer is generally an impact hammer that operates at a rate below 400 blows per minute and generates over 385 foot-pounds of force per blow. The hammer is driven by a power source such as compressed air, steam, or a diesel engine. While such cranes function well to drive large diameter piles into the ground, they are impractical to use for driving needle piles. The forces that an impact hammer generates typically would break a needle pile. Also, it is difficult and time consuming to reposition the large crane apparatus to drive additional piles into the ground. The height of the vertical mast makes it impractical, if not impossible, to use such pile driving cranes at interior pile sites.
Vibratory hammers, which operate at a rate greater than 400 blows per minute, have been used for driving large diameter pile. However, such hammers are used on a crane-like apparatus, which is difficult to maneuver and reposition to drive an array of piles into the ground, and which, due to its size, is limited to exterior applications.
Accordingly, a principal object of the present invention is to provide a hydraulic pile driver that is safe, quick and efficient, and which is relatively compact in size and maneuverable for use in a variety of applications.